The presence of abnormal inclusions of intermediate filaments (IFS) in motor neurons represents a common pathological feature of amyotrophic lateral sclerosis (ALS). The majority of these inclusion bodies are composed of neurofilament (NF) proteins together with peripherin, a type III IF normally expressed at low levels in motor neurons. Recently, we discovered that the overexpression of wild-type peripherin proteins in mice provokes the formation of IF inclusion bodies and late-onset death of motor neurons. Moreover, the disease was precipitated by a deficiency in levels of NF light (NF-L) proteins, a phenomenon associated with ALS. A number of experiments are proposed here to further determine whether peripherin abnormalities may contribute to ALS pathogenesis. We will generate a new transgenic mouse model with the onset of peripherin inclusion formation, modulated by the doxycycline control of transgene expression. We will study the mechanisms regulating the formation and toxicity of peripherin aggregates in neurons. Previous results demonstrated an upregulation of peripherin expression by pro-inflammatory cytokines and by excitotoxic injury. It is proposed, with the use of cultured cells and of transgenic mouse approaches, to further define the regulatory elements activating peripherin gene transcription and to determine whether induction of peripherin levels contributes to neuronal loss after cerebral ischemia and excitotoxic injury. In addition, the gene knockout approach will allow us to determine the contribution of peripherin to pathogenesis in two established mouse models of motor neuron disease, mice expressing mutant superoxide dismutase linked to ALS and mice carrying the wobbler mutation. Finally, we will search for peripherin gene mutations in familial and sporadic cases of ALS.